The primary objective of the research described in this proposal is to establish the nature of the interaction of S-triazine derivatives containing a terminal sulfonyl fluoride moiety with the folate-dependent enzymes serine transhydroxymethylase, methionine synthetase and 5,10-methylenetetrahydrofolate reductase. Initial indications are that these agents become covalently attached to these three enzymes. Experiments will be performed to establish which of these enzymes do become covalently modified. This will involve an analysis of the amino acids and the sequence of active center peptides containing radiolabeled inhibitor. The affinity labeling of these folate enzymes might be partially responsible for the significant antitumor activity displayed by certain S-triazine sulfonyl fluorides such as NSC 127755. In addition to the use of sulfonyl fluoride containing affinity probes, the photoaffinity probes 8-azido-S-adenosylmethionine and 8-azido-S-adenosylhomocysteine will be synthesized and their interaction with methionine synthetase and 5,10-methylenetetrahydrofolate reductase investigated. Again active center peptides will be obtained and characterized. These studies should provide additional insight into the biochemical function of S-adenosylmethionine in methionine biosynthesis and the regulation of 5,10-methylenetetrahydrofolate reductase.